244 IOWA ACADEMY OF SCIENCES. 



plants of the fields to which this is applied will, finally 

 incorporate it into their own tissues after it has been decom- 

 posed by bacteria. As can be readily seen such a system 

 must have several serious disadvantages. First, granting 

 that sewage farming will purify the sewage, which no doubt 

 can be done to a greater or less extent owing to the imposed 

 conditions it is still doubtful whether or not it could be 

 carried on successfully in a great majority of cases. In the 

 first place the land must be of such a character as to per- 

 mit of the irrigation system; secondly, if the sewage were 

 applied continuously, it would be disastrous to the crops, 

 killing them out as well as preventing the nitrification of 

 the sewage by limiting the supply of oxygen to the soil. In 

 the third place, the amount of desirable land required would 

 in many cases be very expensive if it could be obtained at 

 all. Mr. B. S. Brundell, M. Inst. C. E., who has constructed 

 many sewer farms, among them a farm at Dorchester, Eng- 

 land, which is one of the most successful from a sanitary 

 point of view, wrote as follows: "Sewage if properly ap- 

 plied to land may be purified, but the operation is not prof- 

 itable. That is to say, sewage farming cannot, save in ex- 

 ceptional instances, be made to pay." Mr. Brundell also 

 brings up the additional factor of cold winter weather and 

 seriously doubts whether or not the system could be suc- 

 cessfully used in cold countries on account of the protracted 

 cold winter. A very good short account of the Berlin, Ger- 

 many, sewage farm is given by Barwise. 



Chemical precipitation was an effort made on the part 

 of some to entirely purify sewage by the addition of chemi- 

 cals. The principal precipitants used are lime, iron, alumi- 

 num hydrate, alum, and copperas. Although the 

 chemicals used for this purpose are almost innumerable, 

 results tend to show that only the solid matter in suspen- 

 sion is removed, while the sewage is deodorized for the 

 time being. Extensive experiments with chemical pre- 

 cipitation of sewage were made by Mr. Bibden in England 

 as well as by the Massachusetts State Board of Health in 

 America under the supervision and charge of Allen Hazen. 

 The cost of constructing a plant for the chemical precipi- 



